Method for fabricating solar cell

ABSTRACT

A solar cell and method of fabricating the same are provided. The substrate of the solar cell has heavily-doped regions and lightly-doped regions. The anode and the cathode are disposed on the back surface of the substrate, and thus the amount of incident light on the front surface of the substrate is increased. The anode and the cathode are in contact with the heavily doped regions to form selective emitter structure, and thus the contact resistance is reduced. The lightly-doped regions, which are not in contact with the anode and the cathode, have lower saturation current, and thus recombination of hole-electron pairs is reduced, and absorption of infrared light is increased.

BACKGROUND OF THE DISCLOSURE

1. Technical Field

The disclosure relates to a method for fabricating a solar cell, andmore particularly, an interdigitated back electrode solar cell with aselective emitter structure and the method for fabricating it.

2. Description of the Related Art

A solar cell is a photo-electric conversion device which converts solarenergy directly into electrical energy. As supply of our naturalresources such as petroleum declines rapidly, solar energy is the mostpotential alternative energy. However, current solar technology is stilllimited by several obstacles, such as high production cost, complicatedprocess, and low photo-electric conversion efficiency. Therefore, thereare still many obstacles waiting to be overcome in the development ofsolar cell technology.

SUMMARY OF THE DISCLOSURE

It is one of the objectives of the disclosure to provide a method forfabricating a solar cell, thereby boosting the conversion efficiency.

A method for fabricating a solar cell in an embodiment of the disclosureincludes the following steps. A substrate is provided, and the substratehas a first surface and a second surface disposed opposite to the firstsurface. A first patterned doped stacked structure is formed on thesecond surface of the substrate and exposes a portion of the secondsurface of the substrate so as to form at least one first shieldedregion and at least one first exposed region. The first exposed regionhas a first dimension. The first patterned doped stacked structureincludes a first dielectric layer, a first doped layer and a seconddielectric layer. The first doped layer includes a plurality of firstdopants of a first doped type. The first doped layer is disposed betweenthe first dielectric layer and the second dielectric layer. The firstdielectric layer has an opening, and the first doped layer contacts thesecond surface of the substrate through the opening. A second dopedlayer is formed and covers on the first patterned doped stackedstructure and the second surface of the substrate. The second dopedlayer contacts the second surface exposed within the first exposedregion, and the second doped layer includes a plurality of seconddopants of a second doped type opposite to the first doped type. Athermal process is performed to make the first dopants of the firstdoped layer diffuse into the second surface of the substrate so as toform a first lightly-doped region and a first heavily-doped region inthe first shielded region, and to make the second dopants of the seconddoped layer diffuse into the second surface of the substrate so as toform a second heavily-doped region at least in a portion of the firstexposed region. A portion of the first patterned doped stacked structureis removed so as to form a first contact opening exposing the firstheavily-doped region. A portion of the second doped layer is removed soas to form a second contact opening exposing the second heavily-dopedregion. A first electrode is formed in the first contact opening, andthe first electrode is electrically connected to the first heavily-dopedregion. A second electrode is formed in the second contact opening, andthe second electrode is electrically connected to the secondheavily-doped region.

A solar cell in another embodiment of the disclosure includes asubstrate, a first lightly-doped region, a first heavily-doped region, asecond heavily-doped region, a first patterned doped stacked structure,a second doped layer, a first electrode and a second electrode. Thesubstrate has a first surface and a second surface. The second surfaceis disposed opposite to the first surface, and the first surface is alight incident surface. The first lightly-doped region is disposedadjacent to the second surface in the substrate. The first heavily-dopedregion is disposed adjacent to the second surface in the substrate. Bothof the first lightly-doped region and the first heavily-doped regionhave a first doped type. The second heavily-doped region is disposedadjacent to the second surface in the substrate, and the secondheavily-doped region has a second doped type opposite to the first dopedtype. The first patterned doped stacked structure is disposed on thesecond surface of the substrate and corresponds to the firstlightly-doped region. Moreover, the first patterned doped stackedstructure exposes the first heavily-doped region and the secondheavily-doped region. The first patterned doped stacked structureincludes a first dielectric layer, a first doped layer and a seconddielectric layer. The first dielectric layer, the first doped layer andthe second dielectric layer are mutually stacked. The second doped layeris disposed on the first patterned doped stacked structure and thesecond surface in the substrate. The second doped layer exposes aportion of the first heavily-doped region and a portion of the secondheavily-doped region. The first electrode electrically connects thefirst heavily-doped region exposed by the first patterned doped stackedstructure and the second doped layer, and the second electrodeelectrically connects to the second heavily-doped region exposed by thefirst patterned doped stacked structure and the second doped layer.

The solar cell in the disclosure is an interdigitated back electrodesolar cell with a selective emitter structure. Because the electrodecontacts the heavily-doped region of the substrate, the contactresistance in the heavily-doped region of the substrate is lower and thesaturation current in the lightly-doped region not contacting theelectrode is lower. On the other hand, the lightly doped region improvesthe internal reflection of the infrared lights, which improves the lightabsorption of the solar cell. Therefore, the solar cell of thedisclosure has less surface recombination and more electron-holes pairsgenerate, and at the same time, infrared absorption and photo-electricconversion efficiency increase. Comparing to the photo-electricconversion efficiency of a conventional interdigitated back electrodesolar cell, the photo-electric conversion efficiency of the solar cellin the embodiments of the disclosure may further increase about 0.5% toabout 0.6% substantially.

These and other objectives of the disclosure will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-7 are schematic diagrams illustrating the method for fabricatinga solar cell according to a first embodiment of this disclosure.

FIGS. 8-11 are schematic diagrams illustrating the method forfabricating a solar cell according to a second embodiment of thisdisclosure.

FIG. 12 is a diagram illustrating a solar cell according to acomparative embodiment of this disclosure.

DETAILED DESCRIPTION

To provide a better understanding of the disclosure, the embodimentswill be made in detail. The embodiments of the disclosure areillustrated in the accompanying drawings with numbered elements. Inaddition, the terms such as “first” and “second” described in thedisclosure are used to distinguish different components or processes,which do not limit the sequence of the components or processes.

Referring to FIGS. 1-7 are schematic diagrams illustrating the methodfor fabricating a solar cell according to a first embodiment of thisdisclosure. As shown in FIG. 1, a substrate 10 is provided first. Thesubstrate 10 may be a silicon substrate, which is, for example, a singlecrystalline silicon substrate or a polycrystalline silicon substrate,but not limited thereto. The substrate 10 may be any other kind ofsemiconductor substrates (or namely wafers). The thickness of thesubstrate 10 may be, for example, about 50 micrometers (μm) to about 300micrometers (μm), but not limited thereto. The substrate 10 has a firstsurface (or namely front surface) 101 and a second surface (or namelyback surface, rear surface) 102; the second surface 102 is opposite tothe first surface 101, and the first surface 101 is as a light incidentsurface. A saw damage removal (SDR) process is then performed on thesubstrate 10: cleaning the substrate 10 with, for instance, acidic orAlkaline solution, to remove slight damage from the substrate 10.

Then, as shown in FIG. 7, a first patterned doped stacked structure 12is formed on the second surface 102 of the substrate 10 and a portion ofthe second surface 102 of the substrate 10 is exposed. In thisembodiment, the method of forming the first patterned doped stackedstructure 12 is as shown in FIGS. 2-4, but not limited thereto. As shownin FIG. 2, a first dielectric layer 121 is formed on the second surface102 of the substrate 10. The first dielectric layer 121 is patterned toform openings 121A on itself. A portion of the second surface 102 of thesubstrate 10 is exposed through the openings 121A. The first dielectriclayer 121 may be a single-layered or multiple-layered structure, but notlimited thereto. The material of the first dielectric layer 121,preferred, inorganic dielectric materials may be silicon oxide, siliconoxynitride, or silicon nitride, but it may be other appropriate organicor inorganic dielectric materials, for example, alumina. The thicknessof the first dielectric layer 121 is substantially range from 1nanometer (nm) to 20 nanometer (nm), but not limited thereto. The firstdielectric layer 121 may be formed by a chemical vapor deposition (CVD)process, for example, an atmospheric-pressure chemical vapor deposition(APCVD) process, and patterned by, for example, an etching process, butnot limited thereto. The first dielectric layer 121 may also be formedby, for example, a physical vapor deposition process, chemical oxidationprocess, a spin coating process, an ink jet printing process, or ascreen printing process. As shown in FIG. 3, then, a first doped layer122 is formed on the first dielectric layer 121 and the second surface102 of the substrate 10 exposed by the first dielectric layer 121. Thefirst doped layer 122 contacts the second surface 102 of the substrate10 through the openings 121A of the first dielectric layer 121. In otherwords, the first doped layer 122 not only contacts the second surface102 within the openings 121A but also covers the first dielectric layer121. The first doped layer 122 includes a plurality of first dopants (ornamely implants or diffusers) of a first doped type. For example, inthis embodiment, the first doped type may be p-type, the first dopedlayer 122 may be borosilicate glass (BSG), and the dopant may be boron,but not limited thereto. Then, a second dielectric layer 123 is formedon the first doped layer 122; that is to say, the second dielectriclayer 123 covers the first doped layer 122. The thickness of the seconddielectric layer 123 is substantially greater than 100 nm, but notlimited thereto. The second dielectric layer 123 may be a single-layeredor multiple-layered structure, but not limited thereto. The material ofthe second dielectric layer 123, preferred, inorganic dielectricmaterials may be silicon oxide, silicon oxynitride, or silicon nitride,but it may be other appropriate organic or inorganic dielectricmaterials, for example, alumina. The second dielectric layer 123 may beformed by a chemical vapor deposition (CVD) process, for example, anatmospheric-pressure chemical vapor deposition (APCVD) process, but notlimited to this and the second dielectric layer 123 may also be formedby, for example, a physical vapor deposition process, chemical oxidationprocess, a spin coating process, an ink jet printing process, or ascreen printing process. As shown in FIG. 4, after the first dielectriclayer 121, the first doped layer 122 and the second dielectric layer 123are patterned, the first dielectric layer 121, the first doped layer 122and the second dielectric layer 123 are partially removed so as to formthe first patterned doped stacked structure 12. The step to pattern thefirst dielectric layer 121, the first doped layer 122 and the seconddielectric layer 123 may be carried out with an etching process, but notlimited thereto. In other embodiments, the step to pattern the firstdielectric layer 121, the first doped layer 122 and the seconddielectric layer 123 may be carried out with an ink jet printing processand a screen printing process, but without an exposure step and adevelopment step. The first patterned doped stacked structure 12 exposesa portion of the second surface 102 of the substrate 10 and covers aportion of the second surface 102 of the substrate 10. Therefore, atleast one first shielded region 12S is formed on the second surface 102covered by the first patterned doped stacked structure 12, and at leastone first exposed region 12E is formed on the second surface 102 exposedby the first patterned doped stacked structure 12. The first exposedregion 12E has a first dimension. It is worth noting that the openings121A are substantially within the first shielded region 12S.

As shown in FIG. 5, a second doped layer 14 is formed and covers on thefirst patterned doped stacked structure 12 and the second surface 102 ofthe substrate 10. The second doped layer 14 contacts the second surface102 which is exposed within the first exposed region 12E. The seconddoped layer 14 includes a plurality of second dopants of a second dopedtype, and the second doped type is opposite to the first doped type. Forexample, in this embodiment, the second doped type may be n-type, thesecond doped layer 14 may be phosphorosilicate glass (PSG) and thedopant may be phosphorous, but not limited thereto. Moreover, a thirddielectric layer 16 may be formed on the second doped layer 14selectively. The third dielectric layer 16 may be a single-layered ormultiple-layered structure, but not limited thereto. The material of thethird dielectric layer 16, preferred, inorganic dielectric materials maybe silicon oxide, silicon oxynitride, or silicon nitride, but it may beother appropriate organic or inorganic dielectric materials, forexample, alumina. The thickness of the third dielectric layer 16 issubstantially greater than 100 nm, but not limited thereto. The thirddielectric layer 16 may be formed by a chemical vapor deposition (CVD)process, for example, an atmospheric-pressure chemical vapor deposition(APCVD) process, but not limited to this and the third dielectric layer16 may also be formed by, for example, a physical vapor depositionprocess, chemical oxidation process, a spin coating process, an ink jetprinting process, or a screen printing process. The third dielectriclayer 16 is used to promote the insulation of the solar cell, and avoidpoor performance resulting from leakage currents from the anode and thecathode. Therefore, the material, the manufacture process and thethickness of the third dielectric layer 16 depend on the insulatingproperties. A texturing process is carried out to make the first surface101 of the substrate 10 a textured surface, therefore increasing theincident light absorption.

As shown in FIG. 6, a thermal process is performed: the first dopants ofthe first doped layer 122 are diffused into the second surface 102 ofthe substrate 10 so as to form a first lightly-doped region 18L of thefirst doped type and a first heavily-doped region 18H of the first dopedtype in the first shielded region 12S; moreover, the second dopants ofthe second doped layer 14 are diffused into the second surface 102 ofthe substrate 10 so as to form a second heavily-doped region 20H of thesecond doped type in a portion of the first exposed region 12E. In thethermal process mentioned here, the first dopants and the second dopantsare diffused into the selected regions of the substrate 10 respectivelywhen the substrate 10 is at high temperature. Therefore, this kind ofthermal process is also referred to as tempering process or annealingprocess. The first dielectric layer 121 may slow down the diffusion rateand thus has the function of a diffusion barrier. Therefore, in thethermal process, the first heavily-doped region 18H is formed in theportion of the substrate 10 corresponding the openings 121A of the firstdielectric layer 121; in other words, in the thermal process, more ofthe first dopants are diffused into the substrate 10 not covered by thefirst dielectric layer 121, and thus the first heavily-doped region 18His with higher doping concentration. Moreover, with the diffusionbarrier effect of the first dielectric layer 121, less of the firstdopants are diffused into the substrate 10 covered by the firstdielectric layer 121, and thus the first lightly-doped region 18L iswith lower doping concentration. For example, after the thermal process,the surface doping concentration of the first heavily-doped region 18His preferably range from about 10¹⁹atom/cm³ to about 10²¹atom/cm³,substantially; the surface doping concentration of the firstlightly-doped region 18L is preferably range from about 10¹⁸atom/cm³ toabout 10¹⁹atom/cm³, substantially, but not limited thereto. The sheetresistance, or the square resistance, of the first lightly-doped region18L is substantially larger than 80Ω/□ (ohm/square), and sheetresistance of the first heavily-doped region 18H is substantiallysmaller than 50Ω/□ (ohm/square), but not limited thereto. In thisembodiment, the main function of the first dielectric layer 121 in thefirst patterned doped stacked structure 12 is to modify the sheetresistance of the first heavily-doped region 18H and the firstlightly-doped region 18L. Therefore, after the thermal process, in orderto ensure the sheet resistance of the resulting the first heavily-dopedregion 18H and the first lightly-doped region 18L as designed, materialsand manufacture process of the first dielectric layer 121 may beappropriately selected and the thickness of the first dielectric layer121 may be well modified. On the other hand, the first patterned dopedstacked structure 12 may also have the function of the diffusionbarrier; therefore, a second heavily-doped region 20H may be formedwithin the portion of the first exposed region 12E of the substrate 10not covered by the first patterned doped stacked structure 12. That isto say, in the thermal process, the second dopants of the second dopedlayer 14 may be diffused into the first exposed region 12E of thesubstrate 10 not covered by the first patterned doped stacked structure12, thereby leading to high-doping-concentration in the secondheavily-doped region 20H. Since the second dielectric layer 123 of thefirst patterned doped stacked structure 12 is used to prevent the firstdoped layer 122 and the second doped layer 14 from mutually doping, thematerial, manufacture process and thickness should be carefully designedto meet the requirement. With the second dielectric layer 123 disposed,no or little of the second dopants (with negligible concentration oramount) are diffused into the first shielded region 12S covered by thefirst patterned doped stacked structure 12 during the thermal process;in other words, the second dopants are hardly diffused into the firstheavily-doped region 18H and the first lightly-doped region 18L, andthus the doping concentration of the first heavily-doped region 18H andthe first lightly-doped region 18L are rarely changed by the seconddopants. For example, after the thermal process, the surface dopingconcentration of the second heavily-doped region 20H is preferably rangefrom about 10¹⁹atom/cm³ to about 10²¹atom/cm³, substantially, and thesheet resistance of the second heavily-doped region 20H is substantiallysmaller than 50Ω/□ (ohm/square), but not limited thereto. In thisembodiment, the first lightly-doped region 18L and the firstheavily-doped region 18H may have the first doped type, and the secondheavily-doped region 20H may have the second doped type. The substrate10 may be the first doped type or the second doped type according to thedesign of the solar cell. Accordingly, the method for fabricating thesolar cell in this embodiment simultaneously forms the firstlightly-doped region 18L of the first doped type and the firstheavily-doped region 18H of the first doped type, and the secondheavily-doped region 20H of the second doped type all in one singlethermal process.

Moreover, an anti-reflection layer 22 is formed on the first surface 101of the substrate 10. In this embodiment, the anti-reflection layer 22 isformed conformally on the first surface 101 of the substrate 10;therefore, the anti-reflection layer 22 has a texture surface. Theanti-reflection layer 22 can increase the incident light absorption. Theanti-reflection layer 22 may be a single-layered or multiple-layeredstructure, but not limited thereto. The material of the anti-reflectionlayer 22 may be silicon nitride, silicon oxide, silicon oxynitride, orother appropriate material, but not limited thereto. The anti-reflectionlayer 22 may be formed by a plasma-enhanced chemical vapor deposition(PECVD) process, for example, but not limited thereto.

As shown in FIG. 7, a portion of the third dielectric layer 16 and aportion of the first patterned doped stacked structure 12 are removed soas to form a first contact opening 241 exposing the first heavily-dopedregion 18H. In other embodiment, if the second doped layer 14 covers onmajority portion of the first patterned doped stacked structure 12,preferred, the second doped layer 14 covers on all the first patterneddoped stacked structure 12, and then the portion of the third dielectriclayer 16, the portion of the second doped layer 14, and the portion ofthe first patterned doped stacked structure 12 are removed so as to forma first contact opening 241 exposing the first heavily-doped region 18H;a portion of the third dielectric layer 16 and a portion of the seconddoped layer 14 are removed so as to form a second contact opening 242exposing the second heavily-doped region 20H. Then, a first electrode261, such as an anode, is formed in the first contact opening 241 and asecond electrode 262, such as a cathode, is formed in the second contactopening 242. Moreover, the first electrode 261 is electrically connectedto the first heavily-doped region 18H, and the second electrode 262 iselectrically connected to the second heavily-doped region 20H. The solarcell 30 of this embodiment is completed. The first electrode 261 and thefirst heavily-doped region 18H may form a selective emitter structure,and the second electrode 262 and the second heavily-doped region 20H mayform a selective emitter structure. The material of the first electrode261 and the second electrode 262 may be, for example, metal or alloy, orother appropriate material.

Solar cells of this disclosure and methods for fabricating the solarcells are not restricted to the preceding embodiments. Other solar cellsand other feasible methods for fabricating the solar cells will bedisclosed in the following paragraphs. For brevity purposes, like orsimilar features in multiple embodiments will be described with similarreference numerals for ease of illustration and description thereof.

Referring to FIGS. 8-11, and also refer to FIGS. 1-4. FIGS. 8-11 areschematic diagrams illustrating the method for fabricating a solar cellaccording to a second embodiment of this disclosure. The method forfabricating the solar cell of this embodiment continues from the step ofFIG. 4 of the first embodiment. As shown in FIG. 8, after the firstpatterned doped stacked structure 12 is formed, a fourth dielectriclayer 15 is formed on the first patterned doped stacked structure 12 andthe second surface 102 of the substrate 10. Then, the fourth dielectriclayer 15 is patterned so as to cover the first patterned doped stackedstructure 12 and shield a portion of the first exposed region 12E,thereby forming at least one second shielded region 12S′ and at leastone second exposed region 12E′. The second exposed region 12E′ has asecond dimension, and the second dimension of the second exposed region12E′ is smaller than the first dimension of the first exposed region12E—that is to say, the second exposed region 12E′ is located in thefirst exposed region 12E. The fourth dielectric layer 15 may be asingle-layered or multiple-layered structure, but not limited thereto.The material of the fourth dielectric layer 15, preferred, inorganicdielectric materials may be silicon oxide, silicon oxynitride, orsilicon nitride, but it may be other appropriate organic or inorganicdielectric materials, for example, alumina. The thickness of the seconddielectric layer 123, for example, is substantially greater than 100 nm,and the thickness of the fourth dielectric layer 15, for example, issubstantially 1-20 nm, but not limited thereto. The fourth dielectriclayer 15 may be formed by a chemical vapor deposition (CVD) process, forexample, an atmospheric-pressure chemical vapor deposition (APCVD)process, but not limited to this and the fourth dielectric layer 15 mayalso be formed by, for example, a physical vapor deposition process,chemical oxidation process, a spin coating process, an ink jet printingprocess, or a screen printing process.

As shown in FIG. 9, the second doped layer 14 is formed to cover thefourth dielectric layer 15 and the second surface 102 of the substrate10, and the second doped layer 14 contacts the second surface 102 of thesubstrate 10 which is exposed within the second exposed region 12E′.Then, the third dielectric layer 16 is formed on the second doped layer14. A texturing process is carried out to make the first surface 101 ofthe substrate 10 a textured surface, therefore increasing the incidentlight absorption.

As shown in FIG. 10, a thermal process is performed: the first dopantsof the first doped layer 122 are diffused into the second surface 102 ofthe substrate 10 so as to form at least two first lightly-doped regions18L and at least one first heavily-doped region 18H in the firstshielded region 12S; moreover, the second dopants of the second dopedlayer 14 are diffused into the second surface 102 of the substrate 10 soas to form at least one second heavily-doped region 20H in the secondexposed region 12E′, and the second dopants of the second doped layer 14are diffused into the second surface 102 of the substrate 10 so as toform at least two the second lightly-doped regions 20L in the portion ofthe first exposed region 12E outside of the second exposed region 12E′.Preferably, the at least one heavily-doped regions mentioned above arelocated between the at least two of the lightly-doped regions mentionedabove, but not limited thereto. Referring to the illustration about theterm of the thermal process in the previous embodiment for the thermalprocess of this embodiment. The main difference between the method forfabricating the solar cell of this embodiment and that of the firstembodiment is the fourth dielectric layer 15. The fourth dielectriclayer 15 in this embodiment covers a portion of the first exposed region12E, and the fourth dielectric layer 15 also has the diffusion barriereffect. Therefore, in the thermal process, the second heavily-dopedregion 20H of higher doping concentration may be formed in the substrate10 corresponding to the second exposed region 12E′, and the secondlightly-doped region 20L of lower doping concentration may be formed inthe first exposed region 12E of the substrate 10 outside of the secondexposed region 12E′ covered by the fourth dielectric layer 15. Forexample, after the thermal process, the surface doping concentration ofthe first heavily-doped region 18H is preferably range from about10¹⁹atom/cm³ to about 10²¹atom/cm³, substantially; the surface dopingconcentration of the first lightly-doped region 18L is preferably rangefrom about 10¹⁸atom/cm³ to about 10¹⁹atom/cm³, substantially; thesurface doping concentration of the second heavily-doped region 20H ispreferably range from about 10¹⁹atom/cm³ to about 10²¹atom/cm³,substantially; the surface doping concentration of the secondlightly-doped region 20L is preferably range from about 10¹⁸atom/cm³ toabout 10¹⁹atom/cm³, but not limited thereto. The sheet resistance of thefirst heavily-doped region 18H is substantially smaller than 50Ω/□(ohm/square); the sheet resistance of the first lightly-doped region 18Lis substantially larger than 80Ω/□ (ohm/square); the sheet resistance ofthe second heavily-doped region 20H is substantially smaller than 50Ω/□(ohm/square); the sheet resistance of the second lightly-doped region20L is substantially larger than 80Ω/□ (ohm/square), but not limitedthereto. In this embodiment, the main function of the fourth dielectriclayer 15 is to modify the sheet resistance of the second heavily-dopedregion 20H and the sheet resistance of the second lightly-doped region20L. Therefore, in order to ensure the sheet resistance of the resultingthe second heavily-doped region 20H and the resulting secondlightly-doped region 20L as designed after the thermal process,materials and manufacture process of the fourth dielectric layer 15should be appropriately selected and the thickness of the fourthdielectric layer 15 may be well modified. Moreover, an anti-reflectionlayer 22 is formed on the first surface 101 of the substrate 10.Accordingly, the method for fabricating the solar cell in thisembodiment simultaneously forms the first lightly-doped region 18L ofthe first doped type, the first heavily-doped region 18H of the firstdoped type, the second heavily-doped region 20H of the second doped typeand the second lightly-doped region 20L of the second doped type all inone single thermal process.

As shown in FIG. 11, a portion of the third dielectric layer 16, aportion of the fourth dielectric layer 15 and a portion of the firstpatterned doped stacked structure 12 are removed so as to form a firstcontact opening 241 exposing the first heavily-doped region 18H. Inother embodiment, if the second doped layer 14 covers on majorityportion of the fourth dielectric layer 15, preferred, the second dopedlayer 14 covers on all the fourth dielectric layer 15, and then theportion of the third dielectric layer 16, the portion of the seconddoped layer 14, the portion of the fourth dielectric layer 15, and theportion of the first patterned doped stacked structure 12 are removed soas to form a first contact opening 241 exposing the first heavily-dopedregion 18H; a portion of the third dielectric layer 16, a portion of thefourth dielectric layer 15 and a portion of the second doped layer 14are removed so as to form a second contact opening 242 exposing thesecond heavily-doped region 20H. Then, a first electrode 261 is formedin the first contact opening 241 and a second electrode 262 is formed inthe second contact opening 242. Moreover, the first electrode 261 iselectrically connected to the first heavily-doped region 18H, and thesecond electrode 262 is electrically connected to the secondheavily-doped region 20H. The solar cell 40 of this embodiment iscompleted.

Referring to FIG. 12 is a diagram illustrating a solar cell according toa comparative embodiment of this disclosure. As shown in FIG. 12, thesolar cell 50 of the comparative embodiment does not include a selectiveemitter structure. The first lightly-doped region 18L and the secondlightly-doped region 20L are formed in one single semiconductor layer.The first electrode 261 contacts the first lightly-doped region 18L, andthe second electrode 262 contacts the second lightly-doped region 20L.Because, the contact resistance is higher, therefore the solar cell hashigher surface recombination and lower infrared light absorption.

The solar cell in the disclosure is an interdigitated back electrodesolar cell with a selective emitter structure. Because the firstelectrodes 261 and the second electrodes 262 are disposed on the secondsurface 102 of the substrate 10, the incident light absorption to thefirst surface 101 of the substrate 10 increases. Moreover, the firstelectrode 261 contacts the first heavily-doped region 18H and the secondelectrode 262 contacts the second heavily-doped region 20H; therefore,the contact resistance is lower. Since both of the first lightly-dopedregion 18L and the second lightly-doped region 20L, which are lightlydoped, have lower the saturation current, the recombination ofelectron-hole pair reduces, and, at the same time, infrared absorptionand photo-electric conversion efficiency increase. Comparing to thephoto-electric conversion efficiency of the solar cell of thecomparative of the embodiment, the photo-electric conversion efficiencyof the solar cell in the embodiments of the disclosure may furtherincrease about 0.5% to about 0.6% substantially. Moreover, the firstpatterned doped stacked structure is used as the diffusion barrier inthe method for fabricating the solar cell of this disclosure; therefore,with only one single thermal process, the first lightly-doped region ofthe first doped type, the first heavily-doped region of the first dopedtype, the second heavily-doped region of the second doped type and thesecond lightly-doped region of the second doped type are all formed,thereby simplifying manufacturing process and lowering down the cost.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the disclosure. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A method for fabricating a solar cell,comprising: providing a substrate, wherein the substrate has a firstsurface and a second surface disposed opposite to the first surface;forming a first patterned doped stacked structure on the second surfaceof the substrate, and the first patterned doped stacked structureexposing a portion of the second surface of the substrate so as to format least one first shielded region and at least one first exposedregion, wherein the first exposed region has a first dimension, thefirst patterned doped stacked structure comprises a first dielectriclayer, a first doped layer and a second dielectric layer, wherein thefirst dielectric layer, the first doped layer and the second dielectriclayer are mutually stacked, the first doped layer comprises a pluralityof first dopants of a first doped type, the first doped layer isdisposed between the first dielectric layer and the second dielectriclayer, the first dielectric layer has an opening, and the first dopedlayer contacts the second surface of the substrate through the opening;forming a second doped layer covering on the first patterned dopedstacked structure and the second surface of the substrate, wherein thesecond doped layer contacts the second surface exposed within the firstexposed region, and the second doped layer comprises a plurality ofsecond dopants of a second doped type opposite to the first doped type;performing a thermal process to make the first dopants of the firstdoped layer diffuse into the second surface of the substrate so as toform a first lightly-doped region and a first heavily-doped region inthe first shielded region, and to make the second dopants of the seconddoped layer diffuse into the second surface of the substrate so as toform a second heavily-doped region in at least a portion of the firstexposed region; removing a portion of the first patterned doped stackedstructure so as to form a first contact opening exposing the firstheavily-doped region, and removing a portion of the second doped layerso as to form a second contact opening exposing the second heavily-dopedregion; and forming a first electrode in the first contact opening,wherein the first electrode is electrically connected to the firstheavily-doped region, and forming a second electrode in the secondcontact opening, wherein the second electrode is electrically connectedto the second heavily-doped region.
 2. The method for fabricating thesolar cell according to claim 1, wherein a sheet resistance of the firstlightly-doped region is substantially larger than 80 Ω/□, a sheetresistance of the first heavily-doped region is substantially smallerthan 50 Ω/□, and a sheet resistance of the second heavily-doped regionis substantially smaller than 50 Ω/□.
 3. The method for fabricating thesolar cell according to claim 1, further comprising performing atexturing process so as to form a texture surface on the first surfaceof the substrate.
 4. The method for fabricating the solar cell accordingto claim 1, further comprising forming an anti-reflection layer on thefirst surface of the substrate.
 5. The method for fabricating the solarcell according to claim 1, wherein the substrate has the first dopedtype or the second doped type.
 6. The method for fabricating the solarcell according to claim 1, wherein a thickness of the first dielectriclayer is substantially range from 1 nm to 20 nm, and a thickness of thesecond dielectric layer is substantially greater than 100 nm.
 7. Themethod for fabricating the solar cell according to claim 1, furthercomprising forming a third dielectric layer on the second doped layerbefore the thermal process.
 8. The method for fabricating the solar cellaccording to claim 7, wherein a thickness of the third dielectric layeris substantially greater than 100 nm.
 9. The method for fabricating thesolar cell according to claim 1, further comprising forming a fourthdielectric layer on the first patterned doped stacked structure and thesecond surface of the substrate before forming the second doped layer,wherein the fourth dielectric layer covers the first patterned dopedstacked structure and shields a portion of the first exposed region soas to form at least one second shielded region and at least one secondexposed region of a second dimension, the second doped layer contactsthe second surface of the substrate exposed within the second exposedregion, and the second dimension is smaller than the first dimension.10. The method for fabricating the solar cell according to claim 9,further comprising performing the thermal process to make the seconddopants of the second doped layer diffuse into the second surface of thesubstrate so as to form a second lightly-doped region in the secondshielded region and the second heavily-doped region in the secondexposed region.
 11. The method for fabricating the solar cell accordingto claim 9, wherein a thickness of the fourth dielectric layer issubstantially range from 1 nm to 20 nm.
 12. The method for fabricatingthe solar cell according to claim 9, wherein a sheet resistance of thesecond lightly-doped region is substantially larger than 80 Ω/□.